1. Field of Invention
The present invention relates to a distributed video stream decoding system and, in particular, to a distributed video stream decoding system, which distributes the workload of a master decoder to a secondary decoder.
2. Related Art
FIG. 1 shows a structure of the motion picture experts group (MPEG) decoding system. After MPEG system data are sent into a system decoder 100, the data are divided into three groups of data, namely, a video stream, an audio stream, and timing information. The video stream will be transmitted to a video decoder 110 and be decompressed by the video decoder 110 into decompressed video data. The audio stream will be transmitted to an audio decoder 120 and be decompressed by the audio decoder 120 into decompressed audio data. The timing information is used to perform synchronization control over the video decoder 110 and the audio decoder 120.
FIG. 2 shows the structure of a video data steam. The video data steam consists of several picture groups and each picture group contains I, P, B, B, P, B, B pictures, where I is an intra-picture, P is an intra-frame predicted picture, and B is a bi-directional predicted picture. Each picture 130 contains many slices 140, and each slice 140 is composed of several macro-blocks 150. Moreover, each macro-block is formed by four blocks of 8*8 pixels. According to the MPEG specification, if the order of the I, P, and B pictures is I(1), B(2), B(3), P(4), B(5), B(6), and P(7), the order of the video data steam corresponding to the I, P, and B will be I(1), P(4), B(2), B(3), P(7), B(5), and B(6).
Thanks to the progress in high-speed operating CPU (Central Processing Unit), it is forecasted that the CPU operating speed will be over 1.5 GHz this year. Due to the limit on the decoding speed of the H/W (Hardware) MPEG, the idle time of the CPU will become longer if only the H/W MPEG is used to do the MPEG decoding work.